Steam injection has been a unit operation carried out by chemical engineers in processing facilities for as long as chemical engineering has been a science. For example, a typical steam injection water heater was disclosed in U.S. Pat. No. 2,455,498. Subsequently, U.S. Pat. No. 3,984,504 dealt with the fabrication of a rather complex device used to eliminate water hammer which has characterized steam injection systems in the past. It was recognized that such heaters worked satisfactorily at relatively low steam pressure such as at pressures below 300 psi. At high steam pressures, however, water hammer develops due to the sudden collapse of relatively large steam bubbles which are created at high pressures as it condenses within the water.
Steam injection has also been viewed as a preferred expedient in the heat transfer from a first fluid to a moving steam of a liquid commonly employed in food processing. Liquid food products often times must be heated for sterilization and other purposes in an environment which maintains the integrity of the food product free of contamination from the heat source.
Direct steam injection has long been recognized as an exceedingly efficient technique for heating liquids. As steam is injected directly into a liquid, one can realize almost 100 percent of the BTU's in the steam which are absorbed directly into the liquid. Unlike indirect heating by means of, for example, a heat exchanger, there is no condensate retaining unused sensible heat. Because of this high heat-transferability, direct steam injection can save a great deal in energy costs.
Direct steam injection systems offer other benefits as well when compared to heat exchangers and comparable indirect heating systems. A direct steam injection system can provide very accurate temperature control within several degrees Fahrenheit and are efficient in that scale buildup does not become an issue. Systems of this nature also tend to be more compact then comparable heat exchange devices.
There are four basic types of direct steam injection systems, namely, the sparger, the mixing tee, the Venturi and the modulating injection system. The sparger is the simplest system in that it generally consists of nothing more than a perforated pipe discharging steam in a vented storage tank. However, these systems are not without their disadvantages. For example, they must be operated at a set and constant flow rate to prevent the hammering effect observed in steam/water systems. This is the result of operating at steam and water pressures which are at or near equilibrium.
Mixings tees comprise nothing more than steam and waterlines which join a common conduit. Because separate lines are used for each fluid, capital equipment tends to be expensive and inconvenient to install.
Venturi systems are generally more acceptable than those previously discussed, but should be operated under conditions of constant steam pressure, inlet water pressure and outflow demand. If they do not, hammering effect can again be observed as the steam and inlet water pressures approach an equilibrium condition. In addition, changes in these variables can result in varying outlet temperatures which may not be desired.
Prior attempts have even been made to employ static mixers for direct steam injection into a fluid stream. However, as in the other prior approaches, the results have proven spotty with instability and lack of control problems being manifest.
The creation of vibration is a well recognized problem when dealing with direct steam injection. As a consequence, it has been determined that a preferable mixing device would be one capable of reducing vibration in the feed pipes where the mixing takes place. Also, steam injection through static mixing having applicability in mining operations and the like can cause erosion of critical elements. Although static mixing elements, by their very definition, have no moving parts and are thus relatively inexpensive to install and service, when servicing is required, the cost and inconvenience of doing so can be significant as processing lines must be shut down or diverted and various pipelines disconnected in order to gain access to their interiors.
It is thus an object of the present invention to provide a static mixing element in the form of a modular injection system for the introduction of steam to a fluid which minimizes vibration while doing so.
It is yet a further object of the present invention to provide a static mixing element which is more erosion resistant than similar devices of the prior art and when erosion does occur, parts which are worn can be relatively easily replaced.
These and further objects will be more readily apparent when considering the following disclosure and appended claims.